>How long would a fully charged 12v battery last if you left a portable
>colour television on with the use of the inverter?
It depends on:
- the battery capacity when new, usually measured in Ampere-Hours.
- the battery age (capacity of most batteries decreases with age).
- the battery type.
- the inverter efficiency (percentage of power out to power in - typically 80%)
- the power being drawn by the TV.
Assume the TV rating is 24 Watts (24 VA) and it needs 12 volts. That means it draws 24/12 = 2 Amps.
Assume an inverter efficiency of 80%. That means it draws 2.5 Amps from the battery.
Assume the battery rating is 60 Ampere Hours but it is 2 years old so reduce that to 50 AH.
50/2.5 = 20 hours.
I hope this example allows you to work it out for yourself
Other factors are involved (temperature for example) so the calculation is going to give only an approximate idea of what you can expect.
In addition, the battery may be driving other items such as lamps. This must be taken into consideration in the same way. A 24 Watt bulb will draw another 2 Amps.
One final point to consider is that it is not recommended to take a battery below 50% capacity as draining it completely will seriously reduce its life. So half the time calculated.
A typical portable combined VCR/TV might use 55 Watts. That means it draws 55/12 = roughly 4.5 Amps.
50/4.5 = 11 hours. If you want the battery to last, call it 6 hours.
OK, now you can work it out for your own battery and equipment.
>I want to wire two halogen downlighters and one 12 volt Power socket (mini
>cigarette lighter style) into my van. Can you tell me what type of
>cable I need to carry the electrical supply please and give me some rough
>ideas of how to do it?
Downlighters come in various Wattages so you need to decide how bright you need them first of all. Usually 5 Watts, 10 Watts or 20 Watts.
Watts = Volts x Amps
So Amps = Watts/Volts
20 Watts would take nearly 2 Amps from a 12 volt supply.
So the wire must be rated at (minimum) however many Amps the total is. Three x 20W bulbs would take about 5 Amps.
(Amps = 60/12 )
Add to that the number of Amps you want to draw from the Cigar lighter socket.
You should also fit an appropriate fuse at the power source.
Say your total Amps is 10. Then you should use (minimum) 15 Amp insulated (flexible) wire and a 15 Amp fuse to protect it.
